[postgis-devel] 3D Index / 2D Index concerns

[Paul Ramsey]

On Fri, Mar 18, 2011 at 12:06 AM, Paragon Corporation <lr at pcorp.us> wrote:

> Regarding the 2D, 3D index.  You mentioned those have to be separate
> indexes.

If we want the 2D to perform as well as the index it is replacing, it
turns out "yes".

> I guess that means in order to implement the && (2d interacts)  vs.  &&& (3d
> interacts) --- you had have them share separate set of index creation and
> operators?

They are actually two totally different indexes on the same
serialization. The 2D index builds based on a fixed-length key and the
ND index builds based on a variable-length key.

> My main request is that we have an &&& and the 3D index version of && just
> does a 2D check.

The &&& (or whatever we like ##, @@, etc) operator will do an ND
version of the overlaps check.


> 2) Getting to the THIS IS VERY BAD issue.  I don't think our 3D checks make
> provisions for volumetric they are basically checking surface intersection.
> Nicklas can corect me if I am wrong, but I don't see how they
> Can since we can't distinguish right now between volumes and surfaces unless
> we assume all closed surfaces are volumes (which technically isn't correct).

I don't see that this is any different from the current case where the
bounds of a large irregular polygon can easily subsume the bounds of
many many many other smaller polygons nearby. It's sub-optimal, sure,
but it's not a crisis or anything.


P